Coronary CT angiography (CCTA) is an effective tool for predicting heart attack risk in patients with suspected coronary artery disease (CAD) and no medically modifiable cardiac risk factors, according to new research.

Another new study shows that the latest generation of CT scanners can provide excellent image quality at lower radiation doses than those of current scanners. Both studies were published in the May 2013 issue of Radiology.

In the first study, lead author Jonathon Leipsic, M.D., and colleagues at the University of British Columbia, Vancouver, correlated CCTA findings with the risk of major adverse cardiac events like heart attacks in 5,262 individuals with suspected CAD but no medically modifiable risk factors. Using data from the CCTA Evaluation for Clinical Outcomes: An International Multicenter Registry, researchers studied the degree of obstruction within specific cardiac blood vessels and within particular segments of those blood vessels.

After an average follow-up of 2.3 years, 104 patients had experienced a major cardiac event. More than one-quarter of the patients exhibited obstructive disease or disease related to the buildup of plaque in the arteries, while another 12 percent had non-obstructive disease in which less than half of the vessel was blocked.

“Results show that coronary artery disease is quite common even without risk factors,” Dr. Leipsic said. “This scenario comes up often in clinical practice with no good tools to stratify these patients into risk groups.”

CAD patients with narrowing of the arteries on CCTA exhibited a much higher risk of an adverse cardiac event, even with no family history. By contrast, the absence of CAD on CCTA was associated with a very low risk of a major cardiac event. For those whose CCTA results showed no evidence of CAD, the annual risk of a major cardiac event was only 0.31 percent compared with 2.06 percent for those with obstructive disease on CCTA.

“Those without coronary artery disease on CCTA have a good prognosis,” Dr. Leipsic said.

Dr. Leipsic said the results show a potential role for CCTA as a first line test for patients with unusual chest pain. “When patients without a family history and moderating risk factors come in with atypical pain, we’ve shown that CCTA can help identify whether they have a good, medium or bad prognosis and guide more appropriate treatment,” he said. “Based on the location and severity of obstruction, we can identify patients who would derive benefit from surgical revascularization and those who would benefit from medical therapy such as statins.”

Researchers are conducting a five-year follow-up on the study subjects to better understand the association between CCTA findings and long-term prognosis.

“The important take-home message here is that the value of CCTA is underappreciated,” Dr. Leipsic said. “CCTA is the single best noninvasive tool we have for evaluation of the presence or absence of coronary artery disease.”

New CT Scanners Reduce Dose, Maintain Image Quality

In the second study, Marcus Y. Chen, M.D., of the National Institutes of Health in Bethesda, Md., and colleagues used the second generation 320-detector row Aquilion ONE CT scanner from Toshiba Medical Systems to perform CCTA on 107 patients with a mean age 55.4 years. The scanner made its U.S. debut at RSNA 2012 after earning approval from the U.S. Food and Drug Administration (FDA) a month earlier.

“This CT scanner has five times as many detector rows as a standard scanner,” Dr. Chen said. “For the study, we used all the available features including the fastest gantry rotation time and the latest version of iterative reconstruction to reduce image noise and preserve image quality.”

Researchers compared image quality and radiation exposure in millisieverts (mSv) between the new scanner and an older machine. With the new scanner, the effective radiation dose measured 0.93 mSv compared with 2.67 for the older scanner, without sacrificing image quality, Dr. Chen said.

“When we compared the image quality of the new scanner with the old one, it was better in three of four quality metrics,” he said.

The lower radiation dose from the new machine expands the cardiac imaging possibilities for CCTA beyond looking for CAD anatomy, Dr. Chen said. “Since we can significantly reduce radiation, this opens up possible new applications such as cardiac perfusion imaging,” he said. “For example, you could perform a stress test in a CT scanner to examine how well the heart muscle is perfused with blood under stress conditions.”

The new generation scanner would also have applications outside of the heart, Dr. Chen added. “Cardiac is some of the hardest imaging to perform and if you can do that type of imaging successfully, you can image other parts of the body as well,” he said. Researchers are continuing to accrue data and now have information on more than 400 subjects.

Coronary Artery Disease is Focus of Radiology Select, Volume 3

The newest volume of Radiology Select, Volume 3: Coronary Artery Disease, is now available to members and non-members for purchase. The third in the continuing series of selected Radiology articles focusing on a specific subspecialty topic, Radiology Select, Volume 3, features 29 articles covering topics including: